For many years the very high contrast photographic images needed in the graphic arts and printing industries were obtained by developing a `lith` emulsion (usually high in silver chloride content) in a hydroquinone, low sulfite, `lith` developer by the process known as infectious development. However, such low sulfite developers are inherently unstable and are particularly inappropriate for machine processing.
Recently emulsions containing hydrazine nucleating agents have been used and processed in a developer with conventional amounts of sulfite, hydroquinone and possibly metal or a pyrazolidone. Such developers also essentially contain an amine additive as described in U.S. Pat. No. 4,269,929. Other developers containing amines are described in U.S. Pat. Nos. 4,668,605 and 4,740,452.
Many hydrazine nucleating agents have been proposed for use in such materials, for example in U.S. Pat. Nos. 4,323,643, 4,278,748, 4,031,127, 4,030,925, 4,323,643 and 5,104,769.
Copending commonly-assigned U.S. Pat. Application Ser. No. 941,083, filed Oct. 13, 1992, "Photographic High Contrast Silver Halide Materials" by Philip J. Coldrick and Julia Pich describes high contrast photographic silver halide materials, comprising a support bearing a layer of a silver halide emulsion comprising at least 50% silver chloride, sensitized with a dye of defined type which contain in or adjacent the emulsion layer a hydrazine nucleating agent and an amine booster, the combination of which is capable of providing high contrast images.
U.S. Pat. No. 4,999,276 describes photographic materials having a hydrophilic electrically-conductive layer between the support and the silver halide layer(s) which may contain a polymer.
U.S. Pat. No. 5,098,818 describes photographic materials which contain an antihalation hydrophilic colloid underlayer containing a solid particle dye dispersion which may contain polymer. Such materials are limited to those having a total coating weight of hydrophilic colloid on each side of the support of from 0.5 to 3 g/m.sup.2.
During the last ten years, electronic dot-generating scanners for the production of film intermediates for the graphic arts printing process have increased their exposing capabilities, eg by means of sharper beam profiles. This increased accuracy of exposing means calls for an equivalent increase in the accuracy of reproduction obtainable from photographic materials.
It is an object of the present invention to provide such high contrast photographic materials of improved accuracy in image reproduction and, in particular, of scanner-generated dots.